1. Field of the Invention
This invention relates to circuit protection devices comprising PTC conductive polymers.
2. Introduction to the Invention
Conductive polymer and ceramic compositions exhibiting PTC behavior, and electrical devices comprising them, are well known. Reference may be made, for example. to U.S. Pat. Nos. 2,952,761, 2,978,665, 3,243,753, 3,351,882, 3,571,777, 3,757,086, 3,793,716, 3,823,217, 3,858,144, 3,861,029, 3,950,604, 4,017,715, 4,068,281, 4,072,848, 4,085,286, 4,117,312, 4,177,376, 4,177,446, 4,188,276, 4,237,441, 4,242,573, 4,246,468, 4,250,400, 4,252,692, 4,255,698, 4,271,350, 4,272,471, 4,304,987, 4,309,596, 4,309,597, 4,314,230, 4,314,231, 4,315,237, 4,317,027, 4,318,881, 4,327,351, 4,330,704, 4,334,351, 4,352,083, 4,388,607, 4,398,084, 4,413,301, 4,425,397, 4,426,339, 4,426,633, 4,427,877, 4,435,639, 4,429,216, 4,442,139, 4,450,496 4,459,473, 4,459,632, 4,475,012, 4,481,498, 4,476,450 and 4,502,929, 4,514,620 and 4,515,449; J. Applied Polymer Science 19, 813-815 (1975), Klason and Kubat; Polymer Engineering and Science 18, 649-653 (1978), Narkis et al; and commonly assigned U.S. Ser. Nos. 601,424 (Moyer), now abandoned, published as German OLS No. 2,634,999; 750,149 (Kamath et al.), now abandoned, published as German OLS No. 2,755,077; 732,792 (Van Konynenburg et al), now abandoned, published as German OLS No. 2,746,602; 798,154 (Horsma et al), now abandoned, published as German OLS No. 2,821,799; 134,354 (Lutz); 141,984 (Gotcher et al.), published as European Application No. 38718; 141,988 (Fouts et al.), published as European Application No. 38,718, 141,989 (Evans), published as European Application No. 38,713, 141,991 (Fouts et al.), published as European Application No. 38,714, 150,909 (Sopory), published as UK Application No. 2,076,106A, 184,647 (Lutz), 250,491 (Jacobs et al.) 272,854 (Steward et al), published as European Patent Application No. 67,679, 274,010 (Walty et al.), 300,709 and 423,589 (van Konynenburg et al.), published as European Application No. 74,281, 369,309 (Midgley et al.), 483,633 (Wasley), 509,897 and 598,048 (Masia et al.), 524,482 (Tomlinson et al), 534,913 (McKinley), 552,649 (Jensen et al), 573,099 (Batliwalla et al), 904,736, published as UK Pat. Nos. 1,470,502 and 1,470,503, 628,945 (Carlomagno), and 650,918, 650,920 and 650,919 (Batliwalla et al), 716,790 (Carlomagno), 711,908 (Ratell), 711,909 (Deep et al), 711,910 (Au et al) and 711,907 (Ratell). The disclosure of each of the patents, publications and applications to above is incorporated herein by reference.
Particularly useful devices comprising PTC conductive polymers are circuit protection devices. Such devices have a relatively low resistance under the normal operating conditions of the circuit, but are "tripped", i.e., converted into a high resistance state, when a fault condition, e.g., excessive current or temperature, occurs. When the device is tripped by excessive current, the current passing through the PTC element causes it to self heat to an elevated temperature at which it is in a high resistance state. Such devices, and PTC conductive polymer compositions for use in them, are described for example in U.S. Pat. Nos. 4,237,411, 4,238,812; 4,255,698; 4,315,237; 4,317,027; 4.329,726; 4,352,083; 4,413,301; 4,450,496; 4,475,138; 4,481,498; 4,534,889 and 4,562,313 and in copending commonly assigned U.S. application Ser. Nos. 141,989, 711,790 now U.S. Pat. No. 4,685,025, 711,908 now U.S. Pat. No. 4,647,896, 711,909, 711,910, and 711,907 now U.S. Pat. No. 4,647,894. The disclosure of each of these patents and pending applications is incorporated herein by reference.
A particularly important use for circuit protection devices is in telecommunications apparatus, which can be exposed to a variety of different fault conditions. Reference may be made for example to U.S. Pat. Nos. 4,068,277, 4,068,281, 4,475,012, 4,459,632 and 4,562,313. Application Nos. 711,790, 711,907, 711,908, 711,909 and 711,910, the disclosures of which are incorporated hereby by reference.